It has for years been recognized that soil erosion occurs as a result of tilling the soil. Yet, some tillage is highly desirable to increase the retention and absorption of water for the crop to increase crop yield.
Farming practices in those areas where the soil undergoes greater erosion have changed substantially over the last few decades. Very little, if any, moldboard plowing is done in these areas. Chisel plows have become popular, particularly over moldboard plows, because they leave more residue on the surface which prevents runoff of surface soil. Mold-board plows turn the soil, burying the residue. Many farmers have shifted to crop techniques such as minimum tillage (or "direct seeding" as it is sometimes referred to) in order to reduce soil erosion.
In an effort to reduce erosion, it has become desirable to leave as much of the previous crop residue on the soil surface as possible, consistent with the farmer's desire to perform some tillage to increase moisture absorption and retention. Residue on the surface not only holds the soil, but also increases moisture retention. This is particularly important in certain fields which carry the "H.E.L." designation of the U.S. Department of Agriculture (for "highly erodible land").
The desire to leave crop residue in place on the surface of the soil has been made more difficult by the use of tractors capable of conducting tillage operations at ground speeds of up to seven miles per hour. The shank of a typical chisel plow currently available commercially has a thickness of about an inch and a quarter or greater. Because of the thickness, the leading edge of the shank is formed into a tapered wedge to facilitate parting of the soil. The disadvantage of this type of shank is that at ground speeds greater than about two to three miles per hour, the soil and residue at the surface flow around the shank and is displaced laterally, leaving a furrow behind the shank. As it rains, the water gathers in these furrows and the furrows become rivulets. The flowing water carries with it the exposed surface soil in the furrows, thereby creating erosion. At higher speeds, the furrow may be 3-4 inches wide and free of any substantial amount of residue that would help prevent erosion.
There are other disadvantages to some current "state of the art" chisel plows. In chisel plows having parabolic shanks, as distinguished from the flat, rigid shanks of the present invention, the lifting action of the shank increases the depth and width of the furrow formed, and this increases soil erosion. Moreover, designs of current use impact the soil in an effort to pulverize as much of the soil as possible in hopes of increasing moisture retention. However, particularly possible at speeds which many farmers normally operate, the effect is to create more fine particles, rather than larger clods; and this tendency further increases erosion because the "fines" are more easily washed away in heavier downpours.